dwarves/libbtf.c

/*
  SPDX-License-Identifier: GPL-2.0-only

  Copyright (C) 2019 Facebook
 */

#include <fcntl.h>
#include <gelf.h>
#include <limits.h>
#include <malloc.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdarg.h>

#include "libbtf.h"
#include "lib/bpf/include/uapi/linux/btf.h"
#include "lib/bpf/include/linux/err.h"
#include "lib/bpf/src/btf.h"
#include "lib/bpf/src/libbpf.h"
#include "dutil.h"
#include "gobuffer.h"
#include "dwarves.h"
#include "elf_symtab.h"

struct btf *base_btf;
uint8_t btf_elf__verbose;
uint8_t btf_elf__force;

static int btf_var_secinfo_cmp(const void *a, const void *b)
{
	const struct btf_var_secinfo *av = a;
	const struct btf_var_secinfo *bv = b;

	return av->offset - bv->offset;
}

static int libbpf_log(enum libbpf_print_level level, const char *format, va_list args)
{
	return vfprintf(stderr, format, args);
}

int btf_elf__load(struct btf_elf *btfe)
{
	int err;

	libbpf_set_print(libbpf_log);

	/* free initial empty BTF */
	btf__free(btfe->btf);
	if (btfe->raw_btf)
		btfe->btf = btf__parse_raw_split(btfe->filename, btfe->base_btf);
	else
		btfe->btf = btf__parse_elf_split(btfe->filename, btfe->base_btf);

	err = libbpf_get_error(btfe->btf);
	if (err)
		return err;

	return 0;
}

struct btf_elf *btf_elf__new(const char *filename, Elf *elf, struct btf *base_btf)
{
	struct btf_elf *btfe = zalloc(sizeof(*btfe));
	GElf_Shdr shdr;
	Elf_Scn *sec;

	if (!btfe)
		return NULL;

	btfe->in_fd = -1;
	btfe->filename = strdup(filename);
	if (btfe->filename == NULL)
		goto errout;

	btfe->base_btf = base_btf;
	btfe->btf = btf__new_empty_split(base_btf);
	if (libbpf_get_error(btfe->btf)) {
		fprintf(stderr, "%s: failed to create empty BTF.\n", __func__);
		goto errout;
	}

	if (strstarts(filename, "/sys/kernel/btf/")) {
try_as_raw_btf:
		btfe->raw_btf  = true;
		btfe->wordsize = sizeof(long);
		btfe->is_big_endian = BYTE_ORDER == BIG_ENDIAN;
		btf__set_endianness(btfe->btf,
				    btfe->is_big_endian ? BTF_BIG_ENDIAN : BTF_LITTLE_ENDIAN);
		return btfe;
	}

	if (elf != NULL) {
		btfe->elf = elf;
	} else {
		btfe->in_fd = open(filename, O_RDONLY);
		if (btfe->in_fd < 0)
			goto errout;

		if (elf_version(EV_CURRENT) == EV_NONE) {
			fprintf(stderr, "%s: cannot set libelf version.\n",
				__func__);
			goto errout;
		}

		btfe->elf = elf_begin(btfe->in_fd, ELF_C_READ_MMAP, NULL);
		if (!btfe->elf) {
			fprintf(stderr, "%s: cannot read %s ELF file: %s.\n",
				__func__, filename, elf_errmsg(elf_errno()));
			goto errout;
		}
	}

	if (gelf_getehdr(btfe->elf, &btfe->ehdr) == NULL) {
		struct btf_header hdr;
		if (lseek(btfe->in_fd, 0, SEEK_SET) == 0 &&
		    read(btfe->in_fd, &hdr, sizeof(hdr)) == sizeof(hdr) &&
		    hdr.magic == BTF_MAGIC) {
			close(btfe->in_fd);
			elf_end(btfe->elf);
			btfe->in_fd = -1;
			goto try_as_raw_btf;
		}
		if (btf_elf__verbose)
			fprintf(stderr, "%s: cannot get elf header.\n", __func__);
		goto errout;
	}

	switch (btfe->ehdr.e_ident[EI_DATA]) {
	case ELFDATA2LSB:
		btfe->is_big_endian = false;
		btf__set_endianness(btfe->btf, BTF_LITTLE_ENDIAN);
		break;
	case ELFDATA2MSB:
		btfe->is_big_endian = true;
		btf__set_endianness(btfe->btf, BTF_BIG_ENDIAN);
		break;
	default:
		fprintf(stderr, "%s: unknown elf endianness.\n", __func__);
		goto errout;
	}

	switch (btfe->ehdr.e_ident[EI_CLASS]) {
	case ELFCLASS32: btfe->wordsize = 4; break;
	case ELFCLASS64: btfe->wordsize = 8; break;
	default:	 btfe->wordsize = 0; break;
	}

	btfe->symtab = elf_symtab__new(NULL, btfe->elf, &btfe->ehdr);
	if (!btfe->symtab) {
		if (btf_elf__verbose)
			printf("%s: '%s' doesn't have symtab.\n", __func__,
			       btfe->filename);
		return btfe;
	}

	/* find percpu section's shndx */
	sec = elf_section_by_name(btfe->elf, &btfe->ehdr, &shdr, PERCPU_SECTION,
				  NULL);
	if (!sec) {
		if (btf_elf__verbose)
			printf("%s: '%s' doesn't have '%s' section\n", __func__,
			       btfe->filename, PERCPU_SECTION);
		return btfe;
	}
	btfe->percpu_shndx = elf_ndxscn(sec);
	btfe->percpu_base_addr = shdr.sh_addr;
	btfe->percpu_sec_sz = shdr.sh_size;

	return btfe;

errout:
	btf_elf__delete(btfe);
	return NULL;
}

void btf_elf__delete(struct btf_elf *btfe)
{
	if (!btfe)
		return;

	if (btfe->in_fd != -1) {
		close(btfe->in_fd);
		if (btfe->elf)
			elf_end(btfe->elf);
	}

	elf_symtab__delete(btfe->symtab);
	__gobuffer__delete(&btfe->percpu_secinfo);
	btf__free(btfe->btf);
	free(btfe->filename);
	free(btfe);
}

const char *btf_elf__string(struct btf_elf *btfe, uint32_t ref)
{
	const char *s = btf__str_by_offset(btfe->btf, ref);

	return s && s[0] == '\0' ? NULL : s;
}

#define BITS_PER_BYTE 8
#define BITS_PER_BYTE_MASK (BITS_PER_BYTE - 1)
#define BITS_PER_BYTE_MASKED(bits) ((bits) & BITS_PER_BYTE_MASK)
#define BITS_ROUNDDOWN_BYTES(bits) ((bits) >> 3)
#define BITS_ROUNDUP_BYTES(bits) (BITS_ROUNDDOWN_BYTES(bits) + !!BITS_PER_BYTE_MASKED(bits))

static const char * const btf_kind_str[NR_BTF_KINDS] = {
	[BTF_KIND_UNKN]		= "UNKNOWN",
	[BTF_KIND_INT]		= "INT",
	[BTF_KIND_PTR]		= "PTR",
	[BTF_KIND_ARRAY]	= "ARRAY",
	[BTF_KIND_STRUCT]	= "STRUCT",
	[BTF_KIND_UNION]	= "UNION",
	[BTF_KIND_ENUM]		= "ENUM",
	[BTF_KIND_FWD]		= "FWD",
	[BTF_KIND_TYPEDEF]	= "TYPEDEF",
	[BTF_KIND_VOLATILE]	= "VOLATILE",
	[BTF_KIND_CONST]	= "CONST",
	[BTF_KIND_RESTRICT]	= "RESTRICT",
	[BTF_KIND_FUNC]		= "FUNC",
	[BTF_KIND_FUNC_PROTO]	= "FUNC_PROTO",
	[BTF_KIND_VAR]          = "VAR",
	[BTF_KIND_DATASEC]      = "DATASEC",
};

static const char *btf_elf__printable_name(const struct btf_elf *btfe, uint32_t offset)
{
	if (!offset)
		return "(anon)";
	else
		return btf__str_by_offset(btfe->btf, offset);
}

static const char * btf_elf__int_encoding_str(uint8_t encoding)
{
	if (encoding == 0)
		return "(none)";
	else if (encoding == BTF_INT_SIGNED)
		return "SIGNED";
	else if (encoding == BTF_INT_CHAR)
		return "CHAR";
	else if (encoding == BTF_INT_BOOL)
		return "BOOL";
	else
		return "UNKN";
}


__attribute ((format (printf, 5, 6)))
static void btf_elf__log_err(const struct btf_elf *btfe, int kind, const char *name,
			     bool output_cr, const char *fmt, ...)
{
	fprintf(stderr, "[%u] %s %s", btf__get_nr_types(btfe->btf) + 1,
		btf_kind_str[kind], name ?: "(anon)");

	if (fmt && *fmt) {
		va_list ap;

		fprintf(stderr, " ");
		va_start(ap, fmt);
		vfprintf(stderr, fmt, ap);
		va_end(ap);
	}

	if (output_cr)
		fprintf(stderr, "\n");
}

__attribute ((format (printf, 5, 6)))
static void btf_elf__log_type(const struct btf_elf *btfe, const struct btf_type *t,
			      bool err, bool output_cr, const char *fmt, ...)
{
	uint8_t kind;
	FILE *out;

	if (!btf_elf__verbose && !err)
		return;

	kind = BTF_INFO_KIND(t->info);
	out = err ? stderr : stdout;

	fprintf(out, "[%u] %s %s",
		btf__get_nr_types(btfe->btf), btf_kind_str[kind],
		btf_elf__printable_name(btfe, t->name_off));

	if (fmt && *fmt) {
		va_list ap;

		fprintf(out, " ");
		va_start(ap, fmt);
		vfprintf(out, fmt, ap);
		va_end(ap);
	}

	if (output_cr)
		fprintf(out, "\n");
}

__attribute ((format (printf, 5, 6)))
static void btf_log_member(const struct btf_elf *btfe,
			   const struct btf_type *t,
			   const struct btf_member *member,
			   bool err, const char *fmt, ...)
{
	FILE *out;

	if (!btf_elf__verbose && !err)
		return;

	out = err ? stderr : stdout;

	if (btf_kflag(t))
		fprintf(out, "\t%s type_id=%u bitfield_size=%u bits_offset=%u",
			btf_elf__printable_name(btfe, member->name_off),
			member->type,
			BTF_MEMBER_BITFIELD_SIZE(member->offset),
			BTF_MEMBER_BIT_OFFSET(member->offset));
	else
		fprintf(out, "\t%s type_id=%u bits_offset=%u",
			btf_elf__printable_name(btfe, member->name_off),
			member->type,
			member->offset);

	if (fmt && *fmt) {
		va_list ap;

		fprintf(out, " ");
		va_start(ap, fmt);
		vfprintf(out, fmt, ap);
		va_end(ap);
	}

	fprintf(out, "\n");
}

__attribute ((format (printf, 6, 7)))
static void btf_log_func_param(const struct btf_elf *btfe,
			       const char *name, uint32_t type,
			       bool err, bool is_last_param,
			       const char *fmt, ...)
{
	FILE *out;

	if (!btf_elf__verbose && !err)
		return;

	out = err ? stderr : stdout;

	if (is_last_param && !type)
		fprintf(out, "vararg)\n");
	else
		fprintf(out, "%u %s%s", type, name, is_last_param ? ")\n" : ", ");

	if (fmt && *fmt) {
		va_list ap;

		fprintf(out, " ");
		va_start(ap, fmt);
		vfprintf(out, fmt, ap);
		va_end(ap);
	}
}

int32_t btf_elf__add_base_type(struct btf_elf *btfe, const struct base_type *bt,
			       const char *name)
{
	struct btf *btf = btfe->btf;
	const struct btf_type *t;
	uint8_t encoding = 0;
	int32_t id;

	if (bt->is_signed) {
		encoding = BTF_INT_SIGNED;
	} else if (bt->is_bool) {
		encoding = BTF_INT_BOOL;
	} else if (bt->float_type) {
		fprintf(stderr, "float_type is not supported\n");
		return -1;
	}

	id = btf__add_int(btf, name, BITS_ROUNDUP_BYTES(bt->bit_size), encoding);
	if (id < 0) {
		btf_elf__log_err(btfe, BTF_KIND_INT, name, true, "Error emitting BTF type");
	} else {
		t = btf__type_by_id(btf, id);
		btf_elf__log_type(btfe, t, false, true,
				"size=%u nr_bits=%u encoding=%s%s",
				t->size, bt->bit_size,
				btf_elf__int_encoding_str(encoding),
				id < 0 ? " Error in emitting BTF" : "" );
	}

	return id;
}

int32_t btf_elf__add_ref_type(struct btf_elf *btfe, uint16_t kind, uint32_t type,
			      const char *name, bool kind_flag)
{
	struct btf *btf = btfe->btf;
	const struct btf_type *t;
	int32_t id;

	switch (kind) {
	case BTF_KIND_PTR:
		id = btf__add_ptr(btf, type);
		break;
	case BTF_KIND_VOLATILE:
		id = btf__add_volatile(btf, type);
		break;
	case BTF_KIND_CONST:
		id = btf__add_const(btf, type);
		break;
	case BTF_KIND_RESTRICT:
		id = btf__add_restrict(btf, type);
		break;
	case BTF_KIND_TYPEDEF:
		id = btf__add_typedef(btf, name, type);
		break;
	case BTF_KIND_FWD:
		id = btf__add_fwd(btf, name, kind_flag);
		break;
	case BTF_KIND_FUNC:
		id = btf__add_func(btf, name, BTF_FUNC_STATIC, type);
		break;
	default:
		btf_elf__log_err(btfe, kind, name, true, "Unexpected kind for reference");
		return -1;
	}

	if (id > 0) {
		t = btf__type_by_id(btf, id);
		if (kind == BTF_KIND_FWD)
			btf_elf__log_type(btfe, t, false, true, "%s", kind_flag ? "union" : "struct");
		else
			btf_elf__log_type(btfe, t, false, true, "type_id=%u", t->type);
	} else {
		btf_elf__log_err(btfe, kind, name, true, "Error emitting BTF type");
	}
	return id;
}

int32_t btf_elf__add_array(struct btf_elf *btfe, uint32_t type, uint32_t index_type, uint32_t nelems)
{
	struct btf *btf = btfe->btf;
	const struct btf_type *t;
	const struct btf_array *array;
	int32_t id;

	id = btf__add_array(btf, index_type, type, nelems);
	if (id > 0) {
		t = btf__type_by_id(btf, id);
		array = btf_array(t);
		btf_elf__log_type(btfe, t, false, true,
			      "type_id=%u index_type_id=%u nr_elems=%u",
			      array->type, array->index_type, array->nelems);
	} else {
		btf_elf__log_err(btfe, BTF_KIND_ARRAY, NULL, true,
			      "type_id=%u index_type_id=%u nr_elems=%u Error emitting BTF type",
			      type, index_type, nelems);
	}
	return id;
}

int btf_elf__add_member(struct btf_elf *btfe, const char *name, uint32_t type,
			uint32_t bitfield_size, uint32_t offset)
{
	struct btf *btf = btfe->btf;
	const struct btf_type *t;
	const struct btf_member *m;
	int err;

	err = btf__add_field(btf, name, type, offset, bitfield_size);
	t = btf__type_by_id(btf, btf__get_nr_types(btf));
	if (err) {
		fprintf(stderr, "[%u] %s %s's field '%s' offset=%u bit_size=%u type=%u Error emitting field\n",
			btf__get_nr_types(btf), btf_kind_str[btf_kind(t)],
			btf_elf__printable_name(btfe, t->name_off),
			name, offset, bitfield_size, type);
	} else {
		m = &btf_members(t)[btf_vlen(t) - 1];
		btf_log_member(btfe, t, m, false, NULL);
	}
	return err;
}

int32_t btf_elf__add_struct(struct btf_elf *btfe, uint8_t kind, const char *name, uint32_t size)
{
	struct btf *btf = btfe->btf;
	const struct btf_type *t;
	int32_t id;

	switch (kind) {
	case BTF_KIND_STRUCT:
		id = btf__add_struct(btf, name, size);
		break;
	case BTF_KIND_UNION:
		id = btf__add_union(btf, name, size);
		break;
	default:
		btf_elf__log_err(btfe, kind, name, true, "Unexpected kind of struct");
		return -1;
	}

	if (id < 0) {
		btf_elf__log_err(btfe, kind, name, true, "Error emitting BTF type");
	} else {
		t = btf__type_by_id(btf, id);
		btf_elf__log_type(btfe, t, false, true, "size=%u", t->size);
	}

	return id;
}

int32_t btf_elf__add_enum(struct btf_elf *btfe, const char *name, uint32_t bit_size)
{
	struct btf *btf = btfe->btf;
	const struct btf_type *t;
	int32_t id, size;

	size = BITS_ROUNDUP_BYTES(bit_size);
	id = btf__add_enum(btf, name, size);
	if (id > 0) {
		t = btf__type_by_id(btf, id);
		btf_elf__log_type(btfe, t, false, true, "size=%u", t->size);
	} else {
		btf_elf__log_err(btfe, BTF_KIND_ENUM, name, true,
			      "size=%u Error emitting BTF type", size);
	}
	return id;
}

int btf_elf__add_enum_val(struct btf_elf *btfe, const char *name, int32_t value)
{
	struct btf *btf = btfe->btf;
	int err;

	err = btf__add_enum_value(btf, name, value);
	if (!err) {
		if (btf_elf__verbose)
			printf("\t%s val=%d\n", name, value);
	} else {
		fprintf(stderr, "\t%s val=%d Error emitting BTF enum value\n",
			name, value);
	}
	return err;
}

static int32_t btf_elf__add_func_proto_param(struct btf_elf *btfe, const char *name,
					     uint32_t type, bool is_last_param)
{
	int err;

	err = btf__add_func_param(btfe->btf, name, type);
	if (!err) {
		btf_log_func_param(btfe, name, type, false, is_last_param, NULL);
		return 0;
	} else {
		btf_log_func_param(btfe, name, type, true, is_last_param,
				   "Error adding func param");
		return -1;
	}
}

extern struct debug_fmt_ops *dwarves__active_loader;

int32_t btf_elf__add_func_proto(struct btf_elf *btfe, struct cu *cu, struct ftype *ftype, uint32_t type_id_off)
{
	struct btf *btf = btfe->btf;
	const struct btf_type *t;
	struct parameter *param;
	uint16_t nr_params, param_idx;
	int32_t id, type_id;

	/* add btf_type for func_proto */
	nr_params = ftype->nr_parms + (ftype->unspec_parms ? 1 : 0);
	type_id = ftype->tag.type == 0 ? 0 : type_id_off + ftype->tag.type;

	id = btf__add_func_proto(btf, type_id);
	if (id > 0) {
		t = btf__type_by_id(btf, id);
		btf_elf__log_type(btfe, t, false, false, "return=%u args=(%s",
			      t->type, !nr_params ? "void)\n" : "");
	} else {
		btf_elf__log_err(btfe, BTF_KIND_FUNC_PROTO, NULL, true,
			      "return=%u vlen=%u Error emitting BTF type",
			      type_id, nr_params);
		return id;
	}

	/* add parameters */
	param_idx = 0;
	ftype__for_each_parameter(ftype, param) {
		const char *name = dwarves__active_loader->strings__ptr(cu, param->name);

		type_id = param->tag.type == 0 ? 0 : type_id_off + param->tag.type;
		++param_idx;
		if (btf_elf__add_func_proto_param(btfe, name, type_id, param_idx == nr_params))
			return -1;
	}

	++param_idx;
	if (ftype->unspec_parms)
		if (btf_elf__add_func_proto_param(btfe, NULL, 0, param_idx == nr_params))
			return -1;

	return id;
}

int32_t btf_elf__add_var_type(struct btf_elf *btfe, uint32_t type, const char *name,
			      uint32_t linkage)
{
	struct btf *btf = btfe->btf;
	const struct btf_type *t;
	int32_t id;

	id = btf__add_var(btf, name, linkage, type);
	if (id > 0) {
		t = btf__type_by_id(btf, id);
		btf_elf__log_type(btfe, t, false, true, "type=%u linkage=%u",
				  t->type, btf_var(t)->linkage);
	} else {
		btf_elf__log_err(btfe, BTF_KIND_VAR, name, true,
			      "type=%u linkage=%u Error emitting BTF type",
			      type, linkage);
	}
	return id;
}

int32_t btf_elf__add_var_secinfo(struct gobuffer *buf, uint32_t type,
				 uint32_t offset, uint32_t size)
{
	struct btf_var_secinfo si = {
		.type = type,
		.offset = offset,
		.size = size,
	};
	return gobuffer__add(buf, &si, sizeof(si));
}

int32_t btf_elf__add_datasec_type(struct btf_elf *btfe, const char *section_name,
				  struct gobuffer *var_secinfo_buf)
{
	struct btf *btf = btfe->btf;
	size_t sz = gobuffer__size(var_secinfo_buf);
	uint16_t nr_var_secinfo = sz / sizeof(struct btf_var_secinfo);
	struct btf_var_secinfo *last_vsi, *vsi;
	const struct btf_type *t;
	uint32_t datasec_sz;
	int32_t err, id, i;

	qsort(var_secinfo_buf->entries, nr_var_secinfo,
	      sizeof(struct btf_var_secinfo), btf_var_secinfo_cmp);

	last_vsi = (struct btf_var_secinfo *)var_secinfo_buf->entries + nr_var_secinfo - 1;
	datasec_sz = last_vsi->offset + last_vsi->size;

	id = btf__add_datasec(btf, section_name, datasec_sz);
	if (id < 0) {
		btf_elf__log_err(btfe, BTF_KIND_DATASEC, section_name, true,
				 "size=%u vlen=%u Error emitting BTF type",
				 datasec_sz, nr_var_secinfo);
	} else {
		t = btf__type_by_id(btf, id);
		btf_elf__log_type(btfe, t, false, true, "size=%u vlen=%u",
				  t->size, nr_var_secinfo);
	}

	for (i = 0; i < nr_var_secinfo; i++) {
		vsi = (struct btf_var_secinfo *)var_secinfo_buf->entries + i;
		err = btf__add_datasec_var_info(btf, vsi->type, vsi->offset, vsi->size);
		if (!err) {
			if (btf_elf__verbose)
				printf("\ttype=%u offset=%u size=%u\n",
				       vsi->type, vsi->offset, vsi->size);
		} else {
			fprintf(stderr, "\ttype=%u offset=%u size=%u Error emitting BTF datasec var info\n",
				       vsi->type, vsi->offset, vsi->size);
			return -1;
		}
	}

	return id;
}

static int btf_elf__write(const char *filename, struct btf *btf)
{
	GElf_Shdr shdr_mem, *shdr;
	GElf_Ehdr ehdr_mem, *ehdr;
	Elf_Data *btf_data = NULL;
	Elf_Scn *scn = NULL;
	Elf *elf = NULL;
	const void *raw_btf_data;
	uint32_t raw_btf_size;
	int fd, err = -1;
	size_t strndx;

	fd = open(filename, O_RDWR);
	if (fd < 0) {
		fprintf(stderr, "Cannot open %s\n", filename);
		return -1;
	}

	if (elf_version(EV_CURRENT) == EV_NONE) {
		fprintf(stderr, "Cannot set libelf version: %s.\n",
			elf_errmsg(elf_errno()));
		goto out;
	}

	elf = elf_begin(fd, ELF_C_RDWR, NULL);
	if (elf == NULL) {
		fprintf(stderr, "Cannot update ELF file: %s.\n",
			elf_errmsg(elf_errno()));
		goto out;
	}

	elf_flagelf(elf, ELF_C_SET, ELF_F_DIRTY);

	ehdr = gelf_getehdr(elf, &ehdr_mem);
	if (ehdr == NULL) {
		fprintf(stderr, "%s: elf_getehdr failed: %s.\n", __func__,
			elf_errmsg(elf_errno()));
		goto out;
	}

	switch (ehdr_mem.e_ident[EI_DATA]) {
	case ELFDATA2LSB:
		btf__set_endianness(btf, BTF_LITTLE_ENDIAN);
		break;
	case ELFDATA2MSB:
		btf__set_endianness(btf, BTF_BIG_ENDIAN);
		break;
	default:
		fprintf(stderr, "%s: unknown elf endianness.\n", __func__);
		goto out;
	}

	/*
	 * First we look if there was already a .BTF section to overwrite.
	 */

	elf_getshdrstrndx(elf, &strndx);
	while ((scn = elf_nextscn(elf, scn)) != NULL) {
		shdr = gelf_getshdr(scn, &shdr_mem);
		if (shdr == NULL)
			continue;
		char *secname = elf_strptr(elf, strndx, shdr->sh_name);
		if (strcmp(secname, ".BTF") == 0) {
			btf_data = elf_getdata(scn, btf_data);
			break;
		}
	}

	raw_btf_data = btf__get_raw_data(btf, &raw_btf_size);

	if (btf_data) {
		/* Exisiting .BTF section found */
		btf_data->d_buf = (void *)raw_btf_data;
		btf_data->d_size = raw_btf_size;
		elf_flagdata(btf_data, ELF_C_SET, ELF_F_DIRTY);

		if (elf_update(elf, ELF_C_NULL) >= 0 &&
		    elf_update(elf, ELF_C_WRITE) >= 0)
			err = 0;
		else
			fprintf(stderr, "%s: elf_update failed: %s.\n",
				__func__, elf_errmsg(elf_errno()));
	} else {
		const char *llvm_objcopy;
		char tmp_fn[PATH_MAX];
		char cmd[PATH_MAX * 2];

		llvm_objcopy = getenv("LLVM_OBJCOPY");
		if (!llvm_objcopy)
			llvm_objcopy = "llvm-objcopy";

		/* Use objcopy to add a .BTF section */
		snprintf(tmp_fn, sizeof(tmp_fn), "%s.btf", filename);
		close(fd);
		fd = creat(tmp_fn, S_IRUSR | S_IWUSR);
		if (fd == -1) {
			fprintf(stderr, "%s: open(%s) failed!\n", __func__,
				tmp_fn);
			goto out;
		}

		if (write(fd, raw_btf_data, raw_btf_size) != raw_btf_size) {
			fprintf(stderr, "%s: write of %d bytes to '%s' failed: %d!\n",
				__func__, raw_btf_size, tmp_fn, errno);
			goto unlink;
		}

		snprintf(cmd, sizeof(cmd), "%s --add-section .BTF=%s %s",
			 llvm_objcopy, tmp_fn, filename);
		if (system(cmd)) {
			fprintf(stderr, "%s: failed to add .BTF section to '%s': %d!\n",
				__func__, filename, errno);
			goto unlink;
		}

		err = 0;
	unlink:
		unlink(tmp_fn);
	}

out:
	if (fd != -1)
		close(fd);
	if (elf)
		elf_end(elf);
	return err;
}

int btf_elf__encode(struct btf_elf *btfe, uint8_t flags)
{
	struct btf *btf = btfe->btf;

	/* Empty file, nothing to do, so... done! */
	if (btf__get_nr_types(btf) == 0)
		return 0;

	if (btf__dedup(btf, NULL, NULL)) {
		fprintf(stderr, "%s: btf__dedup failed!\n", __func__);
		return -1;
	}

	return btf_elf__write(btfe->filename, btf);
}